Mouse bone marrow and peripheral blood erythroid cell counts are regulated by different autosomal genetic loci

Mouse models for radiation-induced cancers

Potential ionising radiation exposure scenarios are varied, but all bring risks beyond the simple issues of short-term survival. Whether accidentally exposed to a single, whole-body dose in an act of terrorism or purposefully exposed to fractionated doses as part of a therapeutic regimen, radiation exposure carries the consequence of elevated cancer risk. The long-term impact of both intentional and unintentional exposure could potentially be mitigated by treatments specifically developed to limit the mutations and precancerous replication that ensue in the wake of irradiation The development of such agents would undoubtedly require a substantial degree of in vitro testing, but in order to accurately recapitulate the complex process of radiation-induced carcinogenesis, well-understood animal models are necessary. Inbred strains of the laboratory mouse, Mus musculus, present the most logical choice due to the high number of molecular and physiological similarities they share with humans. Their small size, high rate of breeding and fully sequenced genome further increase its value for use in cancer research. This chapter will review relevant m. musculus inbred and F1 hybrid animals of radiation-induced myeloid leukemia, thymic lymphoma, breast and lung cancers. Method of cancer induction and associated molecular pathologies will also be described for each model.

Radiation-induced myeloid leukemia in murine models

The use of radiation therapy is a cornerstone of modern cancer treatment. The number of patients that undergo radiation as a part of their therapy regimen is only increasing every year, but this does not come without cost. As this number increases, so too does the incidence of secondary, radiation-induced neoplasias, creating a need for therapeutic agents targeted specifically towards incidence reduction and treatment of these cancers. Development and efficacy testing of these agents requires not only extensive in vitro testing but also a set of reliable animal models to accurately recreate the complex situations of radiation-induced carcinogenesis. As radiation-induced leukemic progression often involves genomic changes such as rearrangements, deletions, and changes in methylation, the laboratory mouse Mus musculus, with its fully sequenced genome, is a powerful tool in cancer research. This fact, combined with the molecular and physiological similarities it shares with man and its small size and high rate of breeding in captivity, makes it the most relevant model to use in radiation-induced leukemia research. In this work, we review relevant M. musculus inbred and F₁ hybrid animal models, as well as methods of induction of radiation-induced myeloid leukemia. Associated molecular pathologies are also included.

Mouse models of radiation-induced cancers

Radiation-induced (RI) secondary cancers were not a major clinical concern even as little as 15 years ago. However, advances in cancer diagnostics, therapy, and supportive care have saved numerous lives and many former cancer patients are now living for 5, 10, 20, and more years beyond their initial diagnosis. The majority of these patients have received radiotherapy as a part of their treatment regimen and are now beginning to develop secondary cancers arising from normal tissue exposure to damaging effects of ionizing radiation. Because historically patients rarely survived past the extended latency periods inherent to these RI cancers, very little effort was channeled towards the research leading to the development of therapeutic agents intended to prevent or ameliorate oncogenic effects of normal tissue exposure to radiation. The number of RI cancers is expected to increase very rapidly in the near future, but the field of cancer biology might not be prepared to address important issues related to this phenomena. One such issue is the ability to accurately differentiate between primary tumors and de novo arising secondary tumors in the same patient. Another issue is the lack of therapeutic agents intended to reduce such cancers in the future. To address these issues, large-scale epidemiological studies must be supplemented with appropriate animal modeling studies. This work reviews relevant mouse (Mus musculus) models of inbred and F1 animals and methodologies of induction of most relevant radiation-associated cancers: leukemia, lymphoma, and lung and breast cancers. Where available, underlying molecular pathologies are included.

Mouse models for efficacy testing of agents against radiation carcinogenesis—a literature review

As the number of cancer survivors treated with radiation as a part of their therapy regimen is constantly increasing, so is concern about radiation-induced cancers. This increases the need for therapeutic and mitigating agents against secondary neoplasias. Development and efficacy testing of these agents requires not only extensive in vitro assessment, but also a set of reliable animal models of radiation-induced carcinogenesis. The laboratory mouse (Mus musculus) remains one of the best animal model systems for cancer research due to its molecular and physiological similarities to man, small size, ease of breeding in captivity and a fully sequenced genome. This work reviews relevant M. musculus inbred and F₁ hybrid animal models and methodologies of induction of radiation-induced leukemia, thymic lymphoma, breast, and lung cancer in these models. Where available, the associated molecular pathologies are also included.

Quantitative trait loci analysis for peripheral blood parameters in a (BALB/cW × C57BL/6J-Mpl (hlb219)/J) F(2) mice

The genetic basis of the peripheral blood cell parameters is not fully elucidated. Thus, it is essential to research the correlation between blood cell counts levels and the genome in laboratory animals and subsequently in humans. In the present study, we examined 288 F(2) mice from a cross between BALB/cW and C57BL/6J-Mpl(hlb219)/J. The C57BL/6J-Mpl (hlb219)/J strain is a mouse model of thrombocytopenia. We found very strong correlations for PLT counts and revealed some highly significant correlations for RBC counts. On the basis of the obtained results, we presume that genetic control of erythrocyte parameters is divided into two pathways: first, the morphological determinants responsible for the red blood cell count (RBC), hematocrit (HCT), and mean corpuscular volume (MCV), and second, the functional pathway determining the hemoglobin content (HGB). The locus on Chromosome 4 is the only detected quantitative trait locus (QTL) influencing the analyzed platelets parameters. We also detected highly significant correlations for erythrocyte parameters on Chromosome 1 (RBC, MCV, MCH), Chr 7 (HGB), Chr 9 (MCHC), Chr 11 (RBC), and Chr 17 (MCH). Finally, with regards to the given correlations, using the Mouse Genome Database resource, we proposed candidate genes with possible meaning for the level of these parameters: cytokine receptor genes (e.g., Mpl), transcription factor genes (e.g., Xbp1, Ikzf1), hemoglobin chain genes (e.g., Hbb-b1, Hbb-ar), and many others localized in the confidence intervals of found QTLs.

The stromal gene encoding the CD274 antigen as a genetic modifier controlling survival of mice with γ-radiation-induced T-cell lymphoblastic lymphomas

Using an inter-specific subcongenic strain, Nested Recombinant Haplotype 3 (NRH3), generated between two mouse strains showing extreme differences in γ-radiation-induced thymic lymphoma susceptibility (SEG/Pas and C57BL/6J), we have identified a critical region on chromosome 19 that regulates survival of mice suffering from T-cell lymphoblastic lymphomas. Mapped on this region, the gene encoding the Cd274 ligand is able to trigger an inhibitory effect that modulates T-cell receptor (TCR) signalling and affects thymocyte maturation. Interestingly, this gene shows differential expression between thymic stromal cells from both strains in early response to a single sublethal γ-ray dose, but is inhibited in T-cell lymphoblastic lymphomas. Furthermore, we have identified several polymorphisms in the complementary DNA sequence of this gene that affect the affinity for its Cd279 receptor and are able to induce a differential rate of thymocyte apoptosis. Taken together, our data are consistent with Cd274 acting as a genetic modifier that influences the survival of γ-radiation-induced T-cell lymphoma-bearing mice. The data similarly support the idea of a co-evolution of tumour cells and associated stromal cells to generate a favourable microenvironment for T-cell lymphoma growth.

The (non)malignancy of cancerous amino acidic substitutions

The process of natural selection acts both on individual organisms within a population and on individual cells within an organism as they develop into cancer. In this work, we have taken a first step toward understanding the differences in selection pressures exerted on the human genome under these disparate circumstances. Focusing on single amino acid substitutions, we have found that cancer-related mutations (CRMs) are frequent in evolutionarily conserved sites, whereas single amino acid polymorphisms (SAPs) tend to appear in sites having a more relaxed evolutionary pressure. Those CRMs classed as cancer driver mutations show greater enrichment for conserved sites than passenger mutations. Consistent with this, driver mutations are enriched for sites annotated as key functional residues and their neighbors, and are more likely to be located on the surface of proteins than expected by chance. Overall the pattern of CRM and polymorphism is remarkably similar, but we do see a clear signal indicative of diversifying selection for disruptive amino acid substitutions in the cancer driver mutations. The ultimate consequence of the appearance of those mutations must be advantageous for the tumor cell, leading to cell population-growth and migration events similar to those seen in natural ecosystems.

QTL analyses of lineage-negative mouse bone marrow cells labeled with Sca-1 and c-Kit

Differences in the number of functionally and/or phenotypically defined bone marrow cells in inbred mouse strains have been exploited to map quantitative trait loci (QTL) that determine the variation in cell frequency. To extend this approach to the differences in the stem/progenitor cell compartment in CBA/H and C57BL/6 mice, we have exploited the resolution of flow cytometry and the power of QTL analyses in 124 F(2) mice to analyze lineage-negative (Lin(-)) bone marrow cells according to the intensity of labeling with Sca-1 and c-Kit. In the Lin(-) Sca-1(+) c-Kit(+) enriched population, six QTL were identified: one significant and five suggestive. Whereas previous in vitro clonogenic, LTC-IC, day 35 CAFC, and flow cytometry each identified different QTL, our approach identified the same or very similar QTL at all three loci (chromosomes 1, 17, and 18) as well as QTL on chromosomes 6 and 10. In silico analyses implicate hematopoietic stem cell homing involving Cxcr4 and Cxcl12 as being the determining pathway. The mapping of the same or very similar QTL in independent studies using different assay(s) suggests a common genetic determinant, and thus reinforces the biological and genetic significance of the QTL. These data also suggest that mouse bone marrow cell subpopulations can be functionally, phenotypically, and genetically defined.